The ECU is an interesting suspect. The symptoms certainly point in that direction, especially the commonality in the idle jump speed that our bikes share. So, what could go wrong in the ECU? - the bike couldn't have come from the factory like this. - the ECU code is unlikely to age :) - digital logic is also unlikely the age - analog stuff could certainly age, and it's worth cracking the box for a look I'm of the opinion that the bike may have been tuned right on the hairy edge and after some wear in the air/fuel system it triggers this problem. Maybe being able to tune the timing in the ECU could actually "fix" the problem. Perhaps I'm only reiterating what Ben said, but I'm certainly curious to find the root cause. Thanks!

Ben, I share your suspicions about the ECU. And I certainly understand the "carb fatigue" you guys might be feeling at this point. I went through a bit of carb fatigue myself when trying to tune a set of Mikunis for my KH500 after I had it ported. I probably had those carbs off and apart 20+ time before I finally felt like the jetting was right. :-P But IMO, it's probably still worth the time and trouble (assuming you're up for it) to try Ed's experiment with the breather tubes. IIRC, he suggested starting with them long (perhaps as long as a foot) and then gradually trimming them down a bit at a time to see if they make any difference. He was of the opinion that if you tried that, there'd be a good chance you find a "sweet spot" where the stumble was greatly diminished if not eliminated. Having said all this, vent tubing is cheap, but if you've simply got accustomed to riding with the bike as it is, you may (understandably) not feel the need to bother with the experiment at this point.